mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 586

• Manufacturer Part Number: mc9s12e256
• Description: Hcs12 Microcontrollers 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

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Appendix A Electrical Characteristics
A.6.3
Three factors — source resistance, source capacitance and current injection — have an influence on the
accuracy of the ATD.
A.6.3.1
Due to the input pin leakage current as specified in
resistance there will be a voltage drop from the signal source to the ATD input. The maximum source
resistance R
If device or operating conditions are less than worst case or leakage-induced error is acceptable, larger
values of source resistance are allowed.
A.6.3.2
When sampling an additional internal capacitor is switched to the input. This can cause a voltage drop due
to charge sharing with the external and the pin capacitance. For a maximum sampling error of the input
voltage 1LSB, then the external filter capacitor, C
A.6.3.3
There are two cases to consider.
586
Conditions are shown in
Num C
The minimum time assumes a final sample period of 2 ATD clocks cycles while the maximum time assumes a final sample
period of 16 ATD clocks.
Reduced accuracy see
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3
4
5
6
7
1. A current is injected into the channel being converted. The channel being stressed has conversion
D Reference Potential
C Differential Reference Voltage
D ATD Clock Frequency
D ATD 10-Bit Conversion Period
D ATD 8-Bit Conversion Period
D Recovery Time (V
P Reference Supply current
values of 0x3FF (0xFF in 8-bit mode) for analog inputs greater than VRH and 0x000 for values
less than VRL unless the current is higher than specified as disruptive conditions.
S
Factors Influencing Accuracy
Source Resistance
Source Capacitance
Current Injection
specifies results in an error of less than 1/2 LSB (2.5mV) at the maximum leakage current.
Conv, Time at 4.0MHz
Conv, Time at 2.0MHz ATD Clock f
Conv, Time at 2.0MHz ATD Clock f
Table A-4
Table A-22
DDA
=3.3 Volts)
Rating
unless otherwise noted; Supply Voltage 3.3V-10% <= V
Table A-20. 3.3V ATD Operating Characteristics
and
Table
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MC9S12E256 Data Sheet, Rev. 1.08
ATD Clock f
A-23.
Clock Cycles
Clock Cycles
ATDCLK
ATDCLK
ATDCLK
High
Low
Table A-6
f
1
1
1024 * (C
N
V
T
T
Symbol
N
f
T
ATDCLK
RH
CONV10
CONV10
CONV10
CONV8
CONV8
t
V
I
V
REC
REF
RH
RL
-V
and
RL
Table A-7
INS
V
V
DDA
Min
- C
3.0
0.5
3.5
14
12
SSA
—
—
7
6
/2
INN
DDA
in conjunction with the source
).
<= 3.3V+10%
Typ
3.3
—
—
—
—
—
—
—
—
—
—
Freescale Semiconductor
V
0.250
V
Max
DDA
3.6
2.0
28
14
26
13
20
DDA
7
/2
Cycles
Cycles
MHz
Unit
mA
V
V
V
s
s
s
s